The DUP has declined to comment on claims it fines its politicians if they talk to the media without permission. A DUP insider told the BBC's Nolan Show politicians are forced to pay as much as £1,000 if they break internal protocol on dealing with the press.
The DUP said it operated under a constitution and a code of conduct, passed by its executive. The BBC has seen a letter signed by the DUP's chief executive imposing a fine on an elected representative.
While the politician was asked to pay a £100 fine, the BBC understands repeat offenders might face higher charges of £500 or £1,000. The other main Stormont parties all told the BBC they do not impose similar penalties.
The practice of fining elected representatives was "quite unacceptable", said the former chairman of the Committee on Standards in Public Life, as it undermines democracy, and is authoritarian and draconian.
"Elected representatives represent their constituents, even though they have been elected on a particular party ticket, they are there to put over their point of view representing those constituents," said Sir Alastair Graham.
"If they are severely constrained through threats and fines, then that really does undermine their effectiveness," he added.